Stereoscopic photography has been practiced since almost the beginning of photography itself. Early stereoscopic viewers allowed users to view scenic locations with a realism lacking in ordinary photography. Modern versions of stereoscopic viewers, such as the View-Master, produced by Tyco Toys, have long been staples of the toy industry. Advances in technology have produced such variations as "3-D" movies and, more recently, "virtual reality," or computer generated interactive stereoscopic simulations. As real-time stereoscopic viewers are beginning to find uses in such areas as the medical field, it is apparent that stereoscopic viewing is becoming more common.
The optical phenomenon exploited by the brain to extract depth information from a three dimensional scene is known as "parallax." As shown in FIG. 1, a person with two functional eyes 402 viewing point 304 sees slightly different images in each eye 402, due to the slightly different angle from each eye 402 to point 304. The apparent location of point 304 is different in each image formed by eyes 402. By analyzing the differences due to parallax, the brain is able to determine the distance to point 304. By photographing, or otherwise recording, a scene from two distinct locations which mimic the location of eyes 402, as illustrated in FIG. 2, a set of images can be generated which, when viewed properly, can recreate the parallax of the original scene, giving the illusion of three dimensions in the two dimensional images. Each camera 202 uses a lens or lens system 204 to project an image of point 304 onto image plane 308. As illustrated in FIGS. 3a and 3b, each image point 302 of images 300a and 300b represents a point 304 in a three dimensional scene. Each image 300 is associated with a "vantage point" 306, which is the location of the point of view of that image 300. Each image point 302 corresponds to the intersection of an image plane 308 with a "view line" 310. A view line 310 passes through a vantage point 306 and the point 304 in the scene which is represented by image point 302. The view line 310 which passes through a vantage point 306 and intersects image plane 308 perpendicularly defines a "center point" 312 in the image 300 associated with the vantage point 306.
A set of two or more images 300 is "stereoscopic" if they represent substantially parallel views of substantially the same scene, with the vantage points 306 of the images 300 being separated in a direction substantially perpendicular to the direction of the views, this perpendicular direction defining the "epipolar" axis 314.
As illustrated in FIG. 4, when stereoscopic images 300 are viewed with eyes 402 taking the place of vantage points 306 relative to images 300, a viewer perceives apparent points 404 where points 304 had been. Apparent points 404 appear to be at a distance 416 which is proportional to the actual distance 316 of points 304, scaled by the ratio of distance 418 to distance 318, and the ratio of distance 420 to distance 320. Distance 420 is the distance between each of the viewer's eyes 402, and distance 320 is the distance between vantage points 306. Distance 418 is the distance between the viewer's eyes 402 and images 300, and distance 318 is the distance between vantage points 306 and image plane 308.
Stereoscopic systems require the use of at least two stereoscopic images 300 to create the illusion of three dimensional apparent points 404. Graphic images typically contain a large amount of information. Because of this, the storage and transmission of graphic images generally benefit from the use of compression techniques which reduce the amount of information necessary to reconstruct an image. A compressed graphics file contains less information than an uncompressed image, but it can be used to recreate, either perfectly or with losses, the uncompressed image. Because multiple graphic images are required by stereoscopic systems, the image storage and transmission requirements of such systems are twice the image storage and transmission requirements of ordinary monocular images. As such, stereoscopic systems are especially prone to benefit from image compression techniques. What is needed is an image compression technique which is especially suited to stereoscopic images, taking advantage of the high level of redundancy in stereoscopic image sets.